This invention relates to a suspension arrangement for a thermally insulated tank.
A suspension arrangement of this generic type is disclosed in European Patent Document EP 0 014 250 A1. There, the supporting parts are made of holding straps consisting of several individual elements which are connected behind one another and with one another and are made of various fiber materials of different thermal conduction coefficients and different thermal expansion coefficients. The element closest to the tank is made of fiber material with the comparatively lowest thermal expansion coefficient and the comparatively highest thermal conduction coefficient. Despite the division into individual elements of different fiber materials, a construction requiring rather high expenditures, the path for the heat insulation, in the case of low-temperature tanks, is relatively short so that the holding straps still introduce high amounts of heat into the tank. For this reason, individual elements are also thermally shielded with respect to one another by means of cooled insulating layers. Larger temperature differences between the tank shell and the casing structure, in the case of low-temperature tanks, cause a shrinking of the tank shell and a high tensile strain on the fastening parts. In the case of long tanks, the radial shrinking is small relative to the longitudinal shrinking so that length compensation by placing the holding straps in a inclined position is no longer possible.
German Patent Document DE 29 42 164 A1 discloses a wall support for double-walled vessels, specifically Dewar-vessels. These are adjustable supports between the two tank walls for better adjustment and mounting of the double-walled vessel; thus both tank walls are not connected with one another.
It is an object of the invention to develop a suspension arrangement of the above-mentioned type in such a manner that a largely tension-free suspension of the tank is achieved in the casing structure, and at the same time, the heat exchange from the casing structure into the tank and vice versa as a result of the fastening parts is minor.
This object is achieved according to the invention by means of the struts connected with the central part, which together with the tubes between the central part and the tank shell, provide an ideal stiffening of the shell structure as well as of the tank. Thus, in the case of this construction, a thermal shrinking (in the case of low-temperature tanks) or a thermal expansion (in the case of high-temperature tanks) of the tank has no influence on the prestressing of the tank suspension elements. The struts, which extend from the casing structure to the central part, form a long thermal bridge which transports only low quantities of heat from the casing structure to the tank. The loss of tank volume caused by the interior structure amounts only to approximately 1 percent.
In the case of low requirements for torsional rigidity, the central part can be arranged in the tank center, and the struts extend in a star-shape to the casing structure. To improve torsional rigidity, in another embodiment, the central part has a tube centerpiece, four struts respectively extending away from the ends of the tube centerpiece in a star-shape, to the casing structure. The struts may be made of a fiber-reinforced plastic material, for example. This material which, depending on the load, is either fiber-glass-reinforced or carbon-reinforced plastic material, has the advantage of a low heat expansion and a high stability under load. The space between the tubes connecting the central part with the exterior tank wall and the struts may be filled by a thermal insulating material so as to prevent the transmission of cold or heat from the tank toward the outside by way of the struts. Finally, it is possible, in the case of high requirements for torsional rigidity of the whole construction, to arrange tangential struts between the exterior tank wall and the casing structure, tangentially with respect to the exterior tank wall. Because of the relatively low load by which these struts are stressed, their wall thickness may be small. This also considerably reduces the possible heat conduction into the tank.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.